Common fuses are blown out at a predetermined voltage or more to interrupt current. On the contrary, anti-fuse elements have been proposed which are short-circuited to cause a current to flow when a voltage not less than a certain value is applied.
Liquid crystal display devices and various types of lighting devices are equipped with a large number of light-emitting diodes (LED: Light Emitting Diode) as light-emitting sources. In addition, in recent years, various types of electric appliances have electronic circuit boards mounted with a large number of Zener diodes and varistors. In a circuit of these electronic components connected in series with each other, an anti-fuse element is used in electrically parallel connection with each electronic component.
This anti-fuse element is in an insulating state when the electronic components operate normally. When a specific electronic component undergoes disconnection to cause a defective open due to the end of the life or the like, the anti-fuse element is short-circuited into a conducting state. Then, the other electronic components can be avoided from the stop of the operation.
For example, Patent Document 1 discloses an anti-fuse element which is connected in parallel with each of a plurality of LEDs, and provided with low melting point conductors with a predetermined melting point in the vicinity of terminals on each of positive and negative electrode sides. Furthermore, a light-emitting diode lighting circuit is disclosed in which when the LED causes a defective open, the low melting point conductors provided on the anti-fuse element connected in parallel with the LED connect through electric contact between the both terminals.
In Patent Document 1, as shown in FIG. 8(a), an anti-fuse element 101 includes an insulator 103 with a resistive element 102 provided thereon by overcoating or printing, terminals 104, 105 provided on both sides of the insulator 103 and connected to positive and negative electrode sides of the resistive element 102, and low melting point conductors 106, 107 formed on each connection between the insulator 103 and the terminals 104, 105, and in the vicinity of the connection, so as to be fused at a predetermined temperature.
When the LEDs operate normally, the low melting point conductors 106, 107 are separated from each other as shown in FIG. 8(a), and the anti-fuse element 101 thus keeps an electrically insulating state. On the other hand, when the LED causes a defective open due to disconnection or the like, an electric current flows through the anti-fuse element 101. Then, Joule heat is generated in the resistive element 102, and transferred through the insulator 103 to the low melting point conductors 106, 107. As a result, as shown in FIG. 8(b), the low melting point conductors 106, 107 are fused and joined to electrically connect the terminals 104, 105 to each other into a conducting state, and an electric current flows through the anti-fuse element 101 around the LED. This configuration allows, even when some of the LEDs undergo defective opens, the other LEDs connected in series with each other to light normally.
Patent Document 1: Japanese Patent Application Laid-Open No. 2007-329275